SPRITE (signal processing in the element) detectors are three-contact photoconductive structures made of HgCdTe, in which a time-delay-and-integration function is performed in the detector element itself without the n...
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SPRITE (signal processing in the element) detectors are three-contact photoconductive structures made of HgCdTe, in which a time-delay-and-integration function is performed in the detector element itself without the need for external circuitry. Spatial frequency-dependent expressions are developed for the modulation transfer function and the number of equivalent elements Neq of the SPRITE. The development is based on a Green’s function method, which accounts for carrier generation, recombination, and diffusion processes. The usual low-frequency approach of defining a square resolution element on the SPRITE is avoided. The resulting expressions are functions of spatial frequency and are also dependent on physical variables such as the length of the SPRITE element, carrier lifetime, carrier mobility, and operating voltage. These expressions are then applied to the design of a SPRITE element, optimized for operation over a particular range of spatial frequencies.
A modified implantable collamer lens (ICL) with a central hole (diameter 0.36 mm), "Hole-ICL", was created to improve aqueous humour circulation. The aim of this study is to investigate the effects of ICL po...
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A modified implantable collamer lens (ICL) with a central hole (diameter 0.36 mm), "Hole-ICL", was created to improve aqueous humour circulation. The aim of this study is to investigate the effects of ICL power and the relationship between pupil size and modulation-transferfunctions (MTFs) in a Hole-ICL in vitro. The ICL and intraocular lens (IOL) studied were the Collamer ICL (Model ICM, STAAR Surginal) and the monofocal IOL AF-1 (VA-60BBR, HOYA). The ICLs' powers were -20.0 diopters (D), -10.0 D, -5.0 D, +3.0 D, and +10.0 D. A modified ICL with a central hole (diameter 0.36 mm), "Hole-ICL", was created. The monofocal IOL, which was used as an artificial crystalline lens, was +30.0 D in power, and it was 13.0 mm in length with an optic diameter of 6.0 mm. The line-spread function (LSF) was recorded with the OPAL Vector System (Image Science Ltd.), and a model eye (Menicon Co.) was used that consisted of a wet cell. A conventional ICL or Hole-ICL was placed in the posterior chamber of the model eye. The MTF was calculated from the LSF using fast Fourier transform techniques. Furthermore, we investigated the relationship between pupil size and the MTF of the ICL for -5.0 D. The sizes of the effective aperture were 2.0, 3.0, 4.0, and 5.0 mm. The in-focus contrasts of the conventional ICL at 100 cyc/mm for a 3.0-mm effective aperture were 37%, 40%, 39%, 38%, and 39% for -20.0 D, -10.0 D, -5.0 D, +3.0 D, and +10.0 D respectively. The in-focus contrasts of the Hole-ICL at 100 cyc/mm for a 3.0-mm effective aperture were 37%, 40%, 39%, 38%, and 38% for -20.0 D, -10.0 D, -5.0 D, +3.0 D, and +10.0 D respectively. The results for a 2.0-mm effective diameter showed that the in-focus MTF in the Hole-ICL was lower than in the conventional ICL, although the difference was small. These results suggest that differences in MTF between the Hole-ICL and the conventional ICL for various ICL powers and effective pupil diameters were small and clinically negligible.
Pyroelectric infrared sensor arrays are imaging devices for infrared radiation that utilize the temperature dependence of the remanent in polarization in pyroelectric materials. We use the finite element method for th...
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Pyroelectric infrared sensor arrays are imaging devices for infrared radiation that utilize the temperature dependence of the remanent in polarization in pyroelectric materials. We use the finite element method for the calculation of the coupled thermo-electro-mechanical fields for an instance of a linear sensor array, derive the modulation transfer function from the simulation data, and compare the result to an analytical solution.
The aim of this paper is to determine exactly the optical transferfunction corresponding to the time-averaged image-degrading effects of atmospheric turbulence. First the average transferfunction is shown to be rela...
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The aim of this paper is to determine exactly the optical transferfunction corresponding to the time-averaged image-degrading effects of atmospheric turbulence. First the average transferfunction is shown to be related to the spatial coherence function for the light entering the imaging system. Next an exact closed solution is found for the coherence propagation equation. This yields the desired coherence function in terms of the statistics of the random fluctuations of the atmospheric index of refraction. Published meteorological data are analyzed to determine empirical values for the required index statistics. Of particular interest is the variation of turbulent index fluctuations with altitude. Finally, quantitative predictions of image degradation are made and shown to agree with observed data.
This paper describes an original method to measure the modulation transfer function (MTF) of an infrared focal-plane array (IRFPA), based on a diffraction grating called a continuously self-imaging grating (CSIG). We ...
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This paper describes an original method to measure the modulation transfer function (MTF) of an infrared focal-plane array (IRFPA), based on a diffraction grating called a continuously self-imaging grating (CSIG). We give a general methodology to design the test bench, and we describe the data processing approach which has been developed to extract relevant information about the size of the photodiodes and filtering effects. The MTF measurement capability of this method is illustrated with a cooled IRFPA.
This paper describes an original method to measure the modulation transfer function (MTF) of an infrared focal-plane array (IRFPA), based on a diffraction grating called a continuously self-imaging grating (CSIG). We ...
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This paper describes an original method to measure the modulation transfer function (MTF) of an infrared focal-plane array (IRFPA), based on a diffraction grating called a continuously self-imaging grating (CSIG). We give a general methodology to design the test bench, and we describe the data processing approach which has been developed to extract relevant information about the size of the photodiodes and filtering effects. The MTF measurement capability of this method is illustrated with a cooled IRFPA.
When radiographic film is exposed with fluorescent intensifying screens, the spatial x-ray quantum fluctuations are recorded on the film in the form of density fluctuations (“quantum mottle”). The x-ray quantum fluc...
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When radiographic film is exposed with fluorescent intensifying screens, the spatial x-ray quantum fluctuations are recorded on the film in the form of density fluctuations (“quantum mottle”). The x-ray quantum fluctuations can be regarded as the input and the quantum mottle as the output of the image-forming system. The Wiener spectrum of the quantum mottle has been used to determine the relative modulation transfer function of two radiographic systems.
The modulation transfer function (MTF) is a fundamental tool for assessing the sharpness of digital breast tomosynthesis (DBT) systems and is primarily measured using edge devices. We compared the MTF of a Senographe ...
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The modulation transfer function (MTF) is a fundamental tool for assessing the sharpness of digital breast tomosynthesis (DBT) systems and is primarily measured using edge devices. We compared the MTF of a Senographe Pristina DBT system using four-edge devices. These devices were composed of stainless steel with a thickness of 0.6, 0.8, and 1.0 mm, and 1.0 mm tungsten, based on different international guidelines. We evaluated spatial frequencies at MTFs of 0.5 (MTF50%) and 0.1 (MTF10%). The collimator-equipped and non-collimator configurations of the DBT were compared. We found no appreciable differences between scan and chest wall-nipple directions. Both MTF50% (2.90-2.99 cycles/mm) and MTF10% (6.69-6.94 cycles/mm) demonstrated minimal variation across the different edge devices. The collimator-equipped system exhibited an MTF50% that was approximately 5% higher than that of the non-collimator configuration. The choice of the edge device did not appreciably impact the MTF.
Evaluating spatial resolution is an essential work for cone-beam computed tomography (CBCT) manufacturers, prototype designers or equipment users. To investigate the cross-sectional spatial resolution for different tr...
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ISBN:
(纸本)9781510600188
Evaluating spatial resolution is an essential work for cone-beam computed tomography (CBCT) manufacturers, prototype designers or equipment users. To investigate the cross-sectional spatial resolution for different transaxial slices with CBCT, the slanted edge technique with a 3D slanted edge phantom are proposed and implemented on a prototype cone-beam micro-CT. Three transaxial slices with different cone angles are under investigation. An over-sampled edge response function (ERF) is firstly generated from the intensity of the slightly tiled air to plastic edge in each row of the transaxial reconstruction image. Then the oversampled ESF is binned and smoothed. The derivative of the binned and smoothed ERF gives the line spread function (LSF). At last the presampled modulation transfer function (MTF) is calculated by taking the modulus of the Fourier transform of the LSF. The spatial resolution is quantified with the spatial frequencies at 10% MTF level and full-width-half-maximum (FWHM) value. The spatial frequencies at 10% of MTFs are 3.1 +/- 0.08mm(-1), 3.0 +/- 0.05mm(-1), and 3.2 +/- 0.04mm(-1) for the three transaxial slices at cone angles of 3.8 degrees, 0 degrees, and -3.8 degrees respectively. The corresponding FWHMs are 252.8 mu m, 261.7 mu m and 253.6 mu m. Results indicate that cross-sectional spatial resolution has no much differences when transaxial slices being 3.8 degrees away from z=0 plane for the prototype cone beam micro-CT.
A new technique is demonstrated for measurement of modulation transfer function (MTF) on image sensor arrays. Fourier analysis of a low frequency bar target pattern is used to extract MTF at odd harmonics of a target ...
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ISBN:
(纸本)9780819479402
A new technique is demonstrated for measurement of modulation transfer function (MTF) on image sensor arrays. Fourier analysis of a low frequency bar target pattern is used to extract MTF at odd harmonics of a target pattern frequency up to and beyond Nyquist. The technique is particularly useful for linear image arrays (either conventional linescan or time-delay-integration devices) where conventional slanted-edge technique is not always applicable. The technique is well suited to simple implementation and can provide live presentation of the MTF curve, which helps to ensure optimal alignment conditions are achieved. Detailed analysis of the technique and demonstration of experimental results are presented.
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